Descending feedback is a prominent feature of vertebrate sensory systems, yet its importance for neural information processing is not well understood. The objective of this proposal is to determine functional roles of feedback in sensory processing at the levels of cells, local circuits, and behavior. These studies will be carried out in the electrosensory lobe (ELL) of mormyrid electric fish. The ELL is a cerebellum-like structure that integrates incoming sensory signals from electroreceptors with feedback from higher stages in the electrosensory system. Specific aim 1 will determine whether electrosensory feedback is used to generate predictions about the sensory environment. Specific aim 2 will determine whether feedback is crucial for the detection of weak electrosensory signals. Specific aim 3 will determine whether feedback controls spiketiming dependent synaptic plasticity in ELL. The proposed research will be conducted in vivo using intra- and extracellular recordings and behavioral measurements of electrosensory detection thresholds combined with inactivation of feedback. The results are expected to provide insights into how recurrent neural circuitry affects sensory processing.